This invention relates to the architecture of organic light emitting diode devices. Organic light emitting diodes (OLEDs) form light emitting pixels of an OLED device. Referring to FIG. 1, the pixels are formed on a substrate 110, such as a transparent layer of material, for example, glass or plastic. Lower electrodes, such as anodes (not shown), are supported by the substrate 110. The anodes can be formed of a conductive material, such as indium-tin-oxide (ITO). In some types of OLED devices, a pocket layer 125 is formed over the anodes. The pocket structure is typically a layer having apertures or pockets for retaining organic layers (not shown). Each pocket may correspond to an individual pixel of an OLED device. The organic layers, which are layers of conjugated polymers or small-molecules, are deposited into the pockets over the anode. Typically, there are at least two organic layers, a conductive layer and a light emitting layer in each pocket. Other organic layers can also be formed. Upper electrodes, such as cathodes (not shown), sandwich the organic layers with the lower electrodes. The cathodes can be formed of a conductive material, such as a low work function metal, e.g., calcium, barium or aluminum, or a salt, such as lithium fluoride, or a combination thereof. An anode, a cathode and the organic layers therebetween form a pixel.
The OLED device can also include separating structures that act as a shadow structure for forming independent cathodes. Many structuring techniques that might otherwise be used to form individual cathodes, such as metal etching, can adversely affect the organic layers. Therefore, other techniques for ensuring separation between adjacent cathodes are often used. One such technique includes forming pillars or separating structures 160 on the substrate 110 prior to depositing the cathode metal. The cathode metal is applied so that a cathode overlaps one or more pixels and a cathode contact 165. As shown in FIG. 2, the separating structures 160 have a profile that is wider at the top than at the bottom. When the cathode metal is applied, such as by vapor deposition, the metal is deposited between the separating structures 160, forming electrodes, and on top of the separating structures 160. Because the tops of the separating structures 160 shadow the sides from deposited metal, the metal between the pillars 160 cannot contact the metal on top of the pillars.
Referring to FIG. 3, one potential problem posed by using separating structures 160 is if the separating structures 160 deform, such as due to lack of structural integrity or the separating structures 160 having been applied to an uneven surface, the shadowing function of the separating structures 160 may be lost. For example, when the metal layer is deposited over a deformed area 170 of a separating structure 160, a contiguous layer of metal may be formed over the deformed area 170 as well as the adjacent electrodes, thereby electrically connecting two adjacent electrodes across the top of the deformed area 170. When multiple electrodes are connected to one another, the electrodes may no longer be individually addressable or the device can short circuit.
Separating structures can provide for a more accurate placement of the electrodes than a shadow mask. Thus, an improved separating structure can be preferred over other methods of forming electrodes, such as etching or using a mask. However, as described above, there are potential problems with using a separating structure, particularly if the structure fails to perform the job of separating adjacent electrodes from one another. Accordingly, what is needed is a method of forming a device so that the electrodes can be formed and maintained as separate electrodes.